Question: Ben starts counting at 49, and he counts by threes. If 49 is the 1st number that Ben counts. what is the 15th number that he counts?
Solution: What is the first number that he counts? $49$ What is the second number that he counts? $\begin{align*}&49 + 3 \\ &= 52\end{align*}$ What is the third number that he counts? $\begin{align*}&49 + 3 + 3 \\ &= 49 + (2 \times 3) \\ &= 55\end{align*}$ What is the 15th number that he counts? $\begin{align*}&49 + (14\times3) \\ &= 49 + 42 \\ &= 91\end{align*}$